RU2637848C1 - Method for producing high-permeability anisotropic electrical steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: smelting of steel containing copper from 0.4 to 0.6 wt % of copper, casting, hot rolling, etching, two-fold cold rolling with intermediate decarburizing annealing, application of magnesia coating to the strip, high-temperature and straightening annealing. Before the decarburization stage of the strip in the intermediate thickness, it is heated to 700-980°C at a rate of not less than 100°C/s in oxidizing atmosphere and cooling in oxidizing atmosphere to 600-840°C at a rate of not less than 60°C/sec immediately after reaching the maximum temperature at the heating stage.

EFFECT: provide high magnetic permeability of steel and uniformity of magnetic properties.

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Description

The invention relates to ferrous metallurgy and can be used in the manufacture of sheet electrical anisotropic steel (EAS, GO, CGO, RGO, HGO, Hi-B) with a thickness of 0.18-0.50 mm with a texture of (110) [001] (Goss texture, rib texture).

Cold-rolled electrical anisotropic steel is the main soft magnetic material used in modern electrical engineering for the manufacture of cores of various kinds of electrical energy-converting devices [1]. The unique coarse-grained oriented structure of the EAS is formed as a result of a complex technological cycle, including rolling and annealing, one of the final stages of which is high-temperature annealing, during which secondary recrystallization (abnormal grain growth) is realized in steel with the formation of Goss texture - (110) [001] . The main conditions for the realization of abnormal growth in a metal are the prevention of collective recrystallization due to the presence of dispersed particles of the second (inhibitory) phase.

In Russian-language literature, EAS production technology is often called by the type of inhibitor phase used (sulfide, sulfonitride, nitride, etc.) [2, 3]. Currently, EAS with a thickness of 0.18-0.50 mm is produced according to five technology options [2, 3], based on the Goss patent [4]. The bulk of EAS in Russia is produced according to the so-called nitride-copper version, containing 0.4-0.6 wt. % copper [2, 5-7].

Traditionally, EAS largest magnetic induction ₈₀₀ are divided into two classes, normal quality steel with ₈₀₀ <1.88 T (commercial grade, CGO, RGO) and high-permeability steel ₈₀₀ ≥1.88 T (HGO, HI-B) [2, 3 ].

At present, high-permeability steel is produced according to two technological options developed by Nippon Steel. A common condition of these technologies is a single cold rolling with a high degree of deformation. The difference between the options lies in the methods of controlling the inhibitory phase. The first classical sulfonitride technology [7, 8] provides for the formation of the required inhibitory phase (AlN + MnS) during hot rolling, and the second, introduced in the 90s [10-12], is based on the introduction of the main element - nitrogen (to form inhibitor phase AlN) during chemical-thermal treatment in the final thickness (nitriding).

The main disadvantage of the first direction is the need for high-temperature heating of slabs (up to 1400 ° C), which can be realized only on special expensive equipment (furnaces with liquid slag removal, induction slab heaters), which is absent on standard hot rolling mills.

The second direction, firstly, significantly limits the performance of decarburization annealing furnaces and, secondly, involves the use of an environmentally unfavorable ammonia atmosphere.

The disadvantages of both technologies include:

- the need for introducing into the technological cycle the operation of high-temperature (up to 1150 ° C) heat treatment of hot-rolled steel.

Another method for the production of highly permeable anisotropic electrical steel, using a scheme with double cold rolling of metal containing 0.4-0.6 wt. % copper, and the closest set of essential features to the claimed object (prototype) is the production method [13] (RF Patent 2516323 C1. Method for the production of highly permeable anisotropic electrical steel / Tsyrlin MB Applicant Tsyrlin MB [Russia]. 2012148275/02. Published on 05/20/2014. Priority dated 11/14/2012).

The method involves smelting steel, casting to obtain a slab, heating the slab, rough and finish hot rolling, cooling, etching, double cold rolling with intermediate decarburization annealing, applying a magnesia coating to the strip, high-temperature and straightening annealing, and the steel is melted in the following ratio of components wt. %: C 0.018-0.035, Mn 0.10-0.40, Si 3.00-3.50, Al 0.010-0.035, N ₂ 0.008-0.015, Cu 0.40-0.60, the rest is iron and unavoidable impurities , when the ratio between carbon and silicon is selected so that the fraction of austenite during fine hot rolling in the temperature range 1150-1050 ° C is 2-10%, and before final hot rolling, the temperature of the roll is maintained in the range of 1180-1280 ° C and then rolling with a total degree of deformation of 80-95% and with a temperature of the end of rolling of 970-1030 ° C, cooling of the strips after rolling is carried out for a time not exceeding two seconds ND, and heating during high-temperature annealing in the temperature range 400-700 ° C is carried out at a speed of 20-25 ° C / hour. Casting into thin slabs and rolling can be performed on casting and rolling modules. In this case, before finishing rolling is carried out, heating the roll to 1180-1280 ° C in flame or induction furnaces.

The disadvantage of the prototype is the need to maintain before the final hot rolling of the strip temperatures in the range of 1180-1280 ° C and the temperature of the end of the rolling of 970-1030 ° C, which requires either high-temperature heating of the slabs (up to 1400 ° C), or heating of the roll before finishing rolling. Those. EAS production by this method also presupposes the availability of special equipment on hot rolling mills: expensive high-temperature heating furnaces (up to 1400 ° C), flame or induction heating heating furnaces - which significantly limits the development of this technology on standard hot rolling mills.

An additional disadvantage of the prototype in the production of EAS is the limited performance of decarburizing annealing furnaces caused by the processing of metal in an intermediate thickness of 0.50-0.80 mm.

The present invention is to develop a method for the production of sheet EAS with high permeability according to the nitride-copper version of the technology, devoid of the above disadvantages. A distinctive feature of the invention is the rapid heating of the strip in an intermediate thickness before decarburization, followed by rapid cooling.

The proposed method for producing EAS containing copper includes:

1. The smelting of the metal of the following composition, wt. %: C 0.018-0.035, preferably 0.002-0.03, Mn 0.10-0.40, preferably 0.20-0.35, Si 3.0-3.50, preferably 3.15-3.40, Al 0.010-0.035, preferably 0.010-0.025, N ₂ 0.008-0.015, preferably 0.009-0.013, Cu 0.4-0.6, the rest is iron and inevitable impurities;

2. Continuous casting into slabs, including thin slabs on casting and rolling modules;

3. Hot rolling to a thickness of 1.5-3.5 mm, with the completion of deformation at temperatures not lower than 900 ° C and winding into rolls at a temperature not higher than 580 ° C;

4. Cold rolling to an intermediate thickness of 0.50-0.80 mm;

5. Decarburizing annealing of the strip in a humidified nitrogen-hydrogen mixture, comprising a heating step in which a strip in the intermediate thickness is quickly heated to temperatures of 700-980 ° C with a heating rate of at least 100 ° C / s and a cooling step in which the strip is cooled to temperatures 600-850 ° C with a cooling rate of at least 60 ° C / s immediately after reaching the maximum temperature in the heating phase. In this case, rapid heating and cooling enter the heating phase of decarburization annealing and are carried out in an oxygen-free atmosphere;

6. Cold rolling to a thickness of 0.15-0.50 mm;

7. Application of heat-resistant coating;

8. High-temperature annealing with a limitation of the heating rate of the coils in the temperature range 400-700 ° C to 20-25 ° C / h;

9. Rectifier annealing with electrical insulating coating. Hot rolling, cold rolling and other methods in the invention are traditional technical methods in this technical field.

The essence of the proposed technical solution is as follows. It was previously believed that a high degree of perfection and uniformity of the (110) [001] texture in an EAE can be achieved either by the formation of a large amount of a finely dispersed inhibitory phase during hot rolling and heat treatment of the tack, as well as a powerful force effect on the steel texture, which is a single cold rolling (degree of deformation of more than 80%, optimal - 88%). Or, when using double rolling, due to the preservation of the structure and texture of the hot rolled steel, characteristic of the deformed state (with minimal development of recrystallization) due to the parameters of hot rolling and to minimize the volume of phase recrystallization [13]. The authors of the application for the invention of the study showed that the above approaches are not required. High permeability in EAS can be obtained by affecting the structure and inhibitory phase of a metal containing copper (0.4-0.6%), heating parameters at the stage of decarburization annealing in an intermediate thickness.

Conducting rapid heating of a strip in an intermediate thickness in an oxidizing atmosphere to temperatures of 700–980 ° C with a heating rate of at least 100 ° C / s followed by cooling of the heated strip in an oxidizing atmosphere to temperatures of 600–850 ° C with a cooling rate of at least 60 ° C / sec immediately after reaching the maximum temperature during heating, followed by decarburization in a humidified nitrogen-hydrogen mixture, leads to extremely low electromagnetic losses and a high degree of perfection and uniformity of texture (110) [001] in the finished EAS containing copper 0.40-0.60 wt. %

It is known that the presence of copper in electrical steel leads to an increase in the onset temperatures of both primary and secondary recrystallization [14]. Moreover, copper during primary recrystallization complicates both the nucleation process and the direct growth of crystallites free from dislocations. The result is an exacerbation of the octahedral component in the texture of primary recrystallization. An increase in secondary recrystallization temperatures aggravates the rib orientation in the finished steel, i.e. magnetic properties. Moreover, the effect of copper on structural transformations is complex. At the polygonization stage, metastable (existing only in narrow temperature ranges) dispersed phases based on copper that inhibit recrystallization are separated from the supersaturated solid solution. Also, the presence of copper causes the formation of atmospheres or coherent pre-precipitations of copper at dislocations, which lead to a change in the fundamental characteristics of the crystal structure (Peierls barrier and stacking fault energy) and, as a consequence, to the above-mentioned effect on the temperatures of primary and secondary recrystallization.

The application of the claimed technical solution allows you to:

1. Due to the high-speed heating of the strip in the intermediate thickness to temperatures of 700-980 ° C:

1.1 increase the temperature of the onset of primary recrystallization, which, with the above-mentioned mechanisms of copper influence, leads to an increase in the number of nuclei with an acute octahedral orientation favorable for subsequent rolling, and also increases the number of primary recrystallization nuclei with a sharper rib orientation before the second cold rolling.

1.2 quickly dissolve part of aluminum nitrides (AlN) and unstable silicon nitrides (Si ₃ N ₄ ) and, thereby, increase the content and uniformity of the distribution of nitrogen in the α-iron solid solution over the strip thickness.

2. By cooling the heated strip to temperatures of 600-850 ° C with a cooling rate of at least 60 ° C / s immediately after reaching the maximum temperature:

2.1 fix the finely dispersed inhibitory phase of AlN (fix the high-temperature state) and add a part of the new finely dispersed inhibitory phase of AlN, while avoiding the coagulation of the inhibitor;

2.2 to ensure a uniform grain size across the strip section after decarburization (due to the uniform distribution of the finely dispersed phase over the strip thickness) and, as a result, a more uniform secondary recrystallization texture in the final thickness.

Carrying out heating and cooling operations in a non-oxidizing atmosphere avoids excessive oxidation and obtain good surface quality on the finished product.

In fig. 1 shows the production scheme of EAS in accordance with the prototype (a), the production of highly permeable EAS according to the classical sulfonitride technology (b) and the production of EAS containing copper, in accordance with the claimed technical solution (c). The key features of each production scheme are highlighted in bold.

The method can be carried out as follows.

An additional heating section equipped with an induction heater is installed in the industrial unit for decarburization of metal in an intermediate thickness of 0.50-0.80 mm. The size and power of the section is calculated from the need to ensure heating to temperatures of 700-980 ° C with a speed of at least 100 ° C / s followed by decarburization according to the standard mode. If possible, after heating at the outlet of the section, cooling to temperatures of 600-850 ° C with a speed of more than 60 ° C / s is provided immediately after reaching the maximum temperature. In this case, unlike the stage of decarburization annealing of the strip, which is carried out in a humidified nitrogen-hydrogen mixture, induction heating and cooling are carried out in a non-oxidizing atmosphere (for example, in nitrogen protective gas) to suppress excess oxidation and obtain standard surface oxidation parameters after decarburization. The noted solution also allows to significantly increase the performance of metal decarburization units in the intermediate thickness, by reducing the time required to heat the strip, which is usually carried out by flame or electric heating, i.e. increase the effective working length of the furnaces. This additionally eliminates the aforementioned disadvantage of the prototype for the performance of decarburization furnaces in the production of EAS according to the nitride-copper version.

Thus, the technical result of the claimed invention is: 1) the possibility of producing EAS with high permeability, containing 0.4-0.6 wt. % Cu, without using high-temperature heating furnaces during hot rolling (up to 1400 ° С); 2) increasing the performance of metal decarburization units in the intermediate thickness, by reducing the time required to heat the strip.

The following is a description of the experiments conducted by the authors of the present invention. The conditions of the experiments and their results are examples used to confirm the feasibility and results of the present invention, while the present invention is not limited to the examples.

Example 1. Smelted steel with a chemical composition, wt. %: C 0.018-0.035, Mn 0.1-0.4, Si 3.00-3.50, Al 0.01-0.035, N ₂ 0.08-0.015, Cu 0.4-0.6, the rest is iron and inevitable impurities. The resulting slabs were heated, followed by hot rolling, to obtain a hot-rolled strip 2.5 mm thick. The strips were etched and then rolled to a thickness of 0.70 mm in a cold rolling mill.

After rolling, the strips were heated in an induction furnace before decarburization. The speed of the strip was varied to provide different modes of heating and cooling. Then, each strip underwent decarburization annealing in a humid nitrogen-hydrogen atmosphere at a constant temperature of 840 ° С. Further redistribution included a second cold rolling to a thickness of 0.27 mm, applying a magnesia coating, high-temperature annealing at a temperature of 1150 ° C with a limitation of the heating rate of the coils in the temperature range 400-700 ° C to 20-25 ° C / hour. Then, the magnesium oxide residues were washed off the strips and an insulating coating was applied to the previously formed forsterite layer. The corresponding processing modes and results are shown in table 1.

From the data of the table it follows that the application of the claimed technical solution allows to achieve the level of magnetic properties characteristic of high-permeability steel, which is explained by the uniform addition of an additional finely dispersed inhibitory phase and the texture formation processes associated with the presence of copper.

The best magnetic properties were obtained by rapidly heating the strip in an intermediate thickness before decarburization to temperatures of 700-980 ° C with a heating rate of at least 100 ° C / s and cooling to temperatures of 600-850 ° C with a speed of at least 60 ° C / s immediately after reaching the maximum temperature during the heating phase.

Example 2. Strips in an intermediate thickness of 0.65 mm, manufactured by nitride-copper technology, were heated to 840 ° C before decarburization at a heating rate of 10 ° C / s, 22 ° C / s and 225 ° C / s, and immediately after reaching 840 ° C, they were cooled to 750 ° C in less than 1.5 seconds. Then, each strip underwent decarburization annealing in a humid nitrogen-hydrogen atmosphere at a constant temperature of 840 ° С. Further redistribution included a second cold rolling to a thickness of 0.23, 0.27 and 0.30 mm, application of a magnesia coating, high-temperature annealing at a temperature of 1150 ° C with a limitation of the heating rate of the coils in the temperature range 400-700 ° C to 20-25 ° C / hour. Then, the magnesium oxide residues were washed off the strips and an insulating coating was applied to the previously formed forsterite layer. The corresponding processing modes and results are shown in table 2.

From the data of table 2 it follows that the application of the claimed technical solution allows to obtain an unambiguous stable improvement in electromagnetic induction B ₈ and specific losses P _{1.7 / 50} in the EAS containing 0.4-0.6 wt. % copper, for thicknesses of 0.23-0.30 mm.

LITERATURE

1. Kazadzhan LB Magnetic properties of electrical steel and alloys / L.B. Kazadzhan. Ed. V.D. Durneva. M .: LLC “Science and Technology. 2000.224 s.

2. Lobanov M.L., Rusakov G.M., Redikultsev A.A. Electrical anisotropic steel. Part I. History of development // MiTOM. 2011. No7. S. 18-25.

3. Lobanov M.L., Rusakov G.M., Redikultsev A.A. Electrical anisotropic steel. Part II Current state // MiTOM. 2011. No8. S. 3-7.

4. N.P. Goss, US Patent No. 1965559. 07/03/1934.

5. Baryatinsky V.P., Belyaeva G.D., Udovichenko N.V. et al. Study of the structural features of the Fe-3% Si alloy doped with copper // In Sb. Precision alloys in electrical engineering and instrument making. M .: Metallurgy. 1984. S. 33-37.

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13. Tsyrlin M.B. Method for the production of highly permeable anisotropic electrical steel / Applicant M. Tsyrlin [Russia]. RF patent 2516323 C1. Publ. 05/20/2014. Priority 11/14/2012

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Claims (2)

1. Method for the production of electrical anisotropic steel with high permeability, including the smelting of steel containing copper 0.4-0.6 wt. %, casting, hot rolling, etching, double cold rolling with intermediate decarburizing annealing, applying a magnesia coating to the strip, high temperature and straightening annealing, characterized in that before decarburizing annealing, the strip is heated in a non-oxidizing atmosphere to a temperature of 700-980 ° C at a temperature of not less than 100 ° C / s. 2. The method according to p. 1, characterized in that after reaching the maximum heating temperature of the strip it is cooled in a non-oxidizing atmosphere to a temperature of 600-850 ° C at a rate of at least 60 ° C / s, and then subjected to decarburization annealing.

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